Yuan Xing

Hafnium in Aluminum Alloys: A Review

Lots of the available literatures on hafnium in aluminum alloys are reviewed. The new binary Al–Hf phase diagram is simply assessed. Two ternary phase diagrams including Al–Hf–Zr and Al–Hf–Sc are accounted for, with emphasis on the aluminum rich part of the diagrams. The relationship between different structure Al3Hf and several different formation mechanisms including the probable phase transformation mechanisms is described. The continuous Al3Hf phase particles can serve as a grain refiner in the Al melt and a precipitate for controlling the grain structure of the alloy and a strengthening precipitate. A series of effects of Fe, Si, Zr, Sc and Li addition on the behavior of Al3Hf and Al alloys are given. Moreover, the effects of Hf on the microstructure and properties of Al alloys, such as hardness and creep, are reviewed. Finally, some views of Hf-containing Al alloys are summarized.

Growth Directions of Precipitates in the Al-Si-Mg-Hf Alloy Using Combined EBSD and FIB 3D-Reconstruction Techniques.

Nanobelt-like precipitates in an Al-Si-Mg-Hf alloy were studied using electron backscattered diffraction (EBSD) and focused ion beam (FIB) scanning electron microscopy techniques. One grain of the Al matrix with a near [111] normal direction was identified by EBSD and the three-dimensional (3D) microstructure of nanobelt-like precipitates in this grain was studied using 3D-FIB. Ten growth directions of the nanobelt-like precipitates in the grain were identified.

Effect of minor Sc and Zr addition on microstructure and properties of ultra-high strength aluminum alloy

Abstract The Al–9Zn–2.8Mg–2.5Cu– x Zr– y Sc alloys ( x =0, 0.15%, 0.15%; y =0, 0.05%, 0.15%), produced by low-frequent electromagnetic casting technology, were subjected to homogenization treatment, hot extrusion, solution and aging treatment. The effects of minor Sc and Zr addition on microstructure, recrystallization and properties of alloys were studied by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that Sc and Zr addition can refine grains of the as-cast alloy by precipitation of primary Al 3 (Sc,Zr) particles formed during solidification as heterogeneous nuclei. Secondary Al 3 (Sc,Zr) precipitates formed during homogenization treatment strongly pin the movement of dislocation and subgrain boundaries, which can effectively inhibit the alloys recrystallization. Compared with the alloy without Sc and Zr addition, the Al–Zn–Mg–Cu–Zr alloy with 0.05% Sc and 0.15% Zr shows the increase in tensile strength and yield strength by 172 MPa and 218 MPa, respectively. Strengthening comes from the contributions of precipitation, substructure and grain refining.

Microstructure of Al–Si–Mg alloy with Zr/Hf additions during solidification and solution treatment

In this study, the morphology, composition and evolution of intermetallics in Al–7Si–0.3Mg, Al–7Si–0.3Mg–0.47Hf, Al–7Si–0.3Mg–0.16Zr and Al–7Si–0.3Mg–0.14Zr–0.44Hf alloys were characterized by optical microscope (OM), scanning electron microscope (SEM) with energy-dispersive spectrometer (EDS) and transmission electron microscope (TEM). The AlSiZr, AlSiHf and AlSiZrHf phases are formed with additions of Zr and/or Hf in base alloy during solidification, especially the AlZrHf primary particles. The three-dimensional morphology of the AlZrHf particle evolves from 10-polyhedron-like to compressed cube-like during solidification. The new AlZrHf phase experiences partial dissolution after solution treatment, while the others remain in the initial morphology. High Si contents lead to form thermally stable Zr/Hf-rich precipitates in Zr/Hf-containing alloys during solution treatment, especially the nanobelt-like Si2Zr, Si2Hf and Si2(Zr,Hf) precipitates. Particular orientation relationships and the growth mechanism are identified. The finding of the work broadens the elevated temperature application of Al–Si–Mg in modern automotive aluminum engine.